The present invention relates generally to lightning arrestors, and particularly to a fail-safe lightning arrestor for protecting low-voltage, residential-type circuits and their connected loads from the damaging consequences of lightning induced high voltage surges.
Currently available lightning arrestors for installation in residential circuits typically utilize a voltage-dependent resistor, such as a silicon carbide varistor, in series with a spark gap. The presence of the spark gap is prescribed since currently available silicon carbide varistors suitable for lightning arrestor application, being connected from line to neutral in a service entry panelboard, would otherwise draw excessive current at normal line voltage and thus heat up to the point of ultimately destroying itself. Failure of the silicon carbide varistor could then constitute a short circuit with damaging consequences. Since the spark gap has a typical breakdown voltage of 2000 volts, the arrestor affords no overvoltage protection below this level. While voltage surges below 2000 volts do not pose significant harm to wiring and most connected loads, they are potentially damaging to electronic circuitry, particularly solid state electronic circuitry currently utilized in televisions, radios and audio equipment.
Another disadvantage with currently available lightning arrestors resides in the manner of their electrical connection into the circuit to be protected. The arrestor is typically supplied with a plurality of long leads emanating from a case in which the spark gap and varistor are housed. The case must be mounted to the service entry panel enclosure, typically in a knockout, and the lead wires individually connected to the service entry mains and the panel neutral bus. The only convenient places to effect the electrical connections to the mains are either at the line or load terminal connectors of the main circuit protective device, for example, the main circuit breaker. Unfortunately, conventional breaker terminal connectors, such as lugs, are not UL listed for terminating more than one wire. Thus, connecting the lightning arrestor leads into the service entry mains via the main breaker terminal lugs, pursuant to affording voltage surge protection to the entire residential distribution circuit, voids the Underwriters Laboratories listing on the service entry equipment.
Moreover, the typical do-it-yourself homeowner would be reluctant to make arrestor lead terminations at the main breaker terminal connectors, and with good cause as this procedure is potentially hazardous. Thus, an electrician is invariably called upon to install a lightning arrestor. This adds considerably to the expense of lightning protection for residential circuitry, to the point that homeowners all too often elect to forego the protection altogether.
It is accordingly an object of the present invention to provide an improved home lightning arrestor.
An additional object of the present invention is to provide a lightning arrestor of the above character which is effective in protecting wiring and connected loads from both high and low level voltage surges.
A further object is to provide a lightning arrestor of the above character which can be conveniently and safely installed in existing service entry panel enclosures in an approved manner, even by non-electricians.
Still another object is to provide a lightning arrestor of the above character which is fail-safe.
Yet another object is to provide a lightning arrestor of the above character which is reliable in operation, compact in design and inexpensive to manufacture.
Other objects of the invention will in part be obvious and in part appear hereinafter.